Outerworld Arcade

Cinematronics Sound Board Repair:
Star Castle

Summary of Order of Steps to fix a dead Star Castle / any Cinematronics sound board:
1. Visually inspect the board for damage - particularly in the area of R122. If resistors are burnt, test and replace bad transistors and burnt resistors before applying power to the board again.
2. Check to see if your speaker is good. A bad sound board can and will kill a speaker.
3. Check the voltages on the board are good. Replace IC 4 or 5 if your +15, -15 voltages are way off.

Testing the transistors:

After searching for a data sheet on these two components I found that Q17 (2N6292) was an NPN transistor, while Q18 (2N6107) was a PNP transistor. With this information in hand, I referenced the following description on testing transistors with a digital multimeter from Appendix D: of The Cinematronics Vector Monitor Repair Guide:

Test #1
1) Set your meter to the diode test.
2) Connect the red meter lead to the base of the transistor.
3) Connect the black meter lead to the emitter.
A good NPN transistor will read a JUNCTION DROP voltage of between 0.45v and 0.9v. A good PNP transistor will read OPEN.

Test #2
Leave the red meter lead on the base and move the black lead to the collector. The reading should be the same as the previous test.

Test #3
1) Reverse the meter leads in your hands and repeat the test.
2) This time, connect the black meter lead to the base of the transistor.
3) Connect the red meter lead to the emitter.
A good PNP transistor will read a JUNCTION DROP voltage of between 0.45v and 0.9v. A good NPN transistor will read OPEN.

Test #4
Leave the black meter lead on the base and move the red lead to the collector. The reading should be the same as the previous test.

Test #5
Place one meter lead on the collector, the other on the emitter. The meter should read OPEN.
Reverse your meter leads. The meter should read OPEN. This is the same for both NPN and PNP transistors.

Thanks to Randy Fromm <randy@randyfromm.com> for this excellent summary of the diode test method.

Here is a diagram of which leads are the Emitter, Collector and Base on this type of transistor:

To do this test, the transistor must be removed from the circuit.

 

Testing the speaker:

Switch the multimeter to the Ohms/Continuity test.

Place multimeter leads on + and - of speaker inputs.

There should be some resistance (some number near zero).

If test shows no change (open circuit) like the speaker in the image to the right, the speaker is BAD.

NOTE: This can be done with the speaker in circuit - no need to remove the leads to the speaker.

 

Checking for proper voltages on the sound board:

Place black probe of multimeter on connector pin 1 of J1
(white connector)

Then place red probe of multimeter on each of the following pins
to test for proper voltage:

+5v DC: pin 14 on IC 1 : 7414

+25v DC: pin 1 of IC 4 : 7815

+15v DC: pin 3 of IC 4: 7815

-25v DC: pin 2 of IC 5: 7915

-15v DC: pin 3 of IC 5: 7915

 

Repair Log:
I have two dead Star Castle sound boards that I am repairing:

Sound Board #1: Dead
After visual inspection, the first card showed resistor R122 was fried. Resistors R123 & R124 looked like they had taken some heat as well.

Looking at the schematics in the Star Castle manual, I could see that these resistors are in the final amp section of the board. From my experience with the Cinematronics monitors, I know that fried resistors can be caused by a transistor going bad. We need to check and replace any bad transistors before replacing the resistors. There are two in this part of the board, Q17 (2N6292) and Q18 (2N6107).

WARNING:
If your board looks like this, the bad transistors also probably fried your speaker. See below for how to test your speaker. Don't try plugging it into other cabinets or speakers to test it. Until the board is repaired, IT WILL KILL ANY SPEAKER HOOKED UP TO IT.

After testing the two transistors, I found the following:

Q17 (2N6292) - NPN
Test #1 showed OPEN - it should read between 0.45v and 0.9v on a NPN transistor- this showed the transistor was BAD.

Q18 (2N6107) - PNP
Passed all tests except test #5 - the test read 0v - shorted (same as just touching the two probes together) and should read OPEN- this showed the transistor was BAD.

My local electronics parts carries NTE parts. From the online NTE cross-reference page I found that:
2N6292 crosses to NTE196
2N6107 crosses to NTE197
(I didn't need it but BTW:) TLO81 crosses to NTE857M

After getting and installing these parts. I plugged it in and heard - nothing.
Checked voltages - all good.
After reading the experiences fixed these cards in the links below, I checked to see if the speaker was good. The speaker tested as BAD. Plugged in a good speaker and Voila! - Star Castle Sounds!

Sound Card #1 (Again): Fireball sound stuck "on" (07/23/2007)
A few days ago my Star Castle sound board started playing the "fireball" sound constantly whenever the machine was on. After pulling the board and using a logic probe on IC1, a 7414 (Hex inverter with schmitt-trigger inputs), I found that pin 2 was stuck low. The input of pin 1 was low and thus the output of pin 2 should have been high. I replaced the 7414 with a new one (and added a socket for good measure) and the problem was fixed.

Sound Card #2: Dead...
Did the transistor test on Q17 and Q18 as described above. Both transistors tested GOOD. Since there was no physical damage to the board, I probably should have done the following first: Check for proper voltages on the board. All voltages on the board tested good. When I tested the speaker for other sound card found it was BAD. After plugging in this board again with a good speaker I got Star Castle sounds. I'm currently missing the thrust and explosion sounds...